in *.h files, so that the function signatures in the *.h and *.c files fully
match each other.
ut_dulint_sort(): Add a UNIV_INTERN qualifier also to the function definition.
log_block_calc_checksum(), log_block_get_checksum(): Add const qualifiers.
log_block_calc_checksum(): Split a long expression to more readable chunks.
Some compilers might optimize this better.